The present invention relates to a series of novel griseolic acid derivatives, and provides processes for preparing these compounds and methods and compositions using them.
Griseolic acid is a nucleoside-type compound having an adenine base and two carboxylic acid groups. It was first disclosed in, inter alia, European Patent Specification No. 29,329A, but its structure was not, at that stage, known. Its structure was first disclosed in U.S. Pat. No. 4,460,765 (assigned to the present assignees). Certain derivatives of griseolic acid were subsequently disclosed in U.S. patent application Ser. No. 664,866, filed on 25th Oct. 1984 now U.S. Pat. No. 4,634,706, by the present assignees and this also discloses the structure of griseolic acid. Other griseolic acid derivatives, specifically dihydrodesoxygriseolic acid and its salts and esters, are disclosed in U.S. Ser. No. 734,868 filed 16 May 1985 now abandoned.
In accordance with the recommendations of the International Union of Pure and Applied Chemistry (IUPAC), the compounds of the present invention are named as derivatives of griseolic acid (or of dihydrodesoxygriseolic acid), taking griseolic acid as the parent structure. The numbering system employed is shown in U.S. Ser. No. 664,866 (U.S. Pat. No. 4,634,706).
Griseolic acid and the griseolic acid derivatives of U.S. Ser. No. 664,866 and U.S. Ser. No. 734,868, now abandoned, as well as the derivatives of the present invention, have the ability to inhibit the activity of phosphodiesterases specific to various cyclic nucleotides, for example 3',5'-cyclic adenosine monophosphate (cAMP), phosphodiesterase (PDE) or 3',5'-cyclic guanosine monophosphate (cGMP) PDE, and can thus increase the level of the cyclic nucleotide, e.g. cAMP or cGMP, in the cells of a patient treated with such a compound.
It is well known that cAMP, which is very widely distributed in animal tissues, functions as a second messenger for and mediates the effect of a large number of hormones; as a result, cAMP has a variety of very important pnysiological and biochemical roles. Additionally, it is known to have an effect on or participate in: division, proliferation and differentiation of cells; the systolic system, particularly myocardia; haematopoiesis; various activities of the central nervous system; immune reactions; and the liberation of insulin and histamine. Its concentration in tissues, and hence its effect upon these various functions, depends upon the balance between the enzyme which synthesizes cAMP (i.e. adenylate cyclase) and the enzyme which decomposes cAMP, cAMP PDE. An inhibitor against cAMP PDE would increase the level of cAMP in the cells and is thus expected to have a variety of therapeutic uses, for example: in the treatment of cardiovascular problems; as an antiasthmatic agent; as a smooth muscle relaxant; as a psychotropic or neurotropic agent; as an anti-inflammatory agent; in the therapy of cancer; and as a treatment for diabetes.
The activities of other cyclic nucleotides, e.g. cGMP, have, to date, been less comprehensively investigated. However, it is believed that they nave a range of activities similar to, albeit not identical with, those of cAMP. Hence, inhibition of the PDE's specific to such other cyclic nucleotides will give rise to a range of therapeutic effects similar to those arising from the inhibition of cAMP PDE. As the activities of such other cyclic nucleotides are elucidated, the need will arise for inhibitors of the PDE's associated with those other nucleotides, which inhibitors show a greater specificity to one or other of the PDE's of the other nucleotides, rather than cAMP PDE; indeed, development of such inhibitors may even assist or encourage investigation of such other cyclic nucleotides.
In addition to griseolic acid and its derivatives, other compounds known to inhibit the PDE's of cAMP and cGMP include papaverine, dipyridamole and some compounds related to the constituent bases of nucleic acids, such as theophylline or M & B 22,948 [Kukovetz et al., Naunyn-Schmiedeberg's Arch. Pharmakol., 310, 129 (1979)].
We have now discovered a series of compounds which are related to griseolic acid and to dihydrodesoxygriseolic acid and which share the activity of griseolic acid and dihydrodesoxygriseolic acid. Certain of these compounds surprisingly have a greater activity against cGMP PDE than against cAMP PDE. Certain compounds of the invention, whilst retaining the desirable activity are of more value as intermediates in the preparation of other, related compounds.